Method and apparatus for replacing the function of facet joints

ABSTRACT

A system and method is provided for replacing the functions of a facet joint between a superior vertebra and an inferior vertebra without necessarily requiring an anatomical implant. The method includes: providing one or more flexible posterior devices to replace main functions of the facet joint; and adapting a first one of the one or more posterior devices for a first attachment to a first pedicle, and a second attachment to a second pedicle.

The present disclosure relates to spinal devices and methods, and moreparticularly, to a system and method for replacing the functions of afacet joint between a superior vertebra and an inferior vertebra withoutnecessarily requiring an anatomical implant.

BACKGROUND

A vertebrae includes a vertebral body and posteriorly extendingstructures including pedicles, a lamina, articular processes, and aspinous process. The articular processes include superior and inferiorprocesses that join to form zygapophyseal, or facet joints, withadjacent vertebrae. The facet joints are formed by the articularprocesses of adjacent vertebrae—the inferior articular process of avertebra articulates with the superior articular process of the vertebrabelow. Facet joints perform several functions, including stabilizing thespine and earring approximately 20% of the compressive load on thespine. Accordingly, their anatomic position and orientation affect themobility of each spinal region. For example, in the cervical region,facet joints are oriented in the coronal plane and are capable of asignificant range of motions in the six degrees of freedom. In thelumber area, facet joints are oriented parasagittal and thereby limitrotation.

Major trauma or repetitive minor trauma may cause a facet joint to bedamaged or otherwise degenerate. As a result, the hyaline cartilage thatlines the joint can lose its water content, and eventually become worn.When this happens, the articular processes begin to override each otheras the joint capsules become stretched, resulting in the malalignment ofthe joints and abnormal biomechanical function of the motion segment.

The current treatment for degenerated or otherwise damaged facet jointsis to provide prosthetic facet joints. The prosthetic facet joints areshaped and positioned similar to the original facet joint, and must beconstructed to withstand the required movement and weight handlingfunctions of the original facet joint. Such requirements are difficultto achieve while also meeting requirements of reliability anddurability. What is needed is a system and method for reducing and/oreliminating the need for anatomical prosthetic facet joints.

SUMMARY

The present invention provides a system and method for replacing thefunctions of a facet joint between a superior vertebra and an inferiorvertebra without necessarily requiring an anatomical implant.

In one embodiment, a surgical implant for replacing functions of a facetjoint between adjacent vertebrae is provided. The surgical implantincludes a first biocompatible attachment device for attaching to afirst pedicle of a superior vertebrae and a second biocompatibleattachment device for attaching to a second pedicle of an inferiorvertebrae. The surgical implant also includes a flexible member attachedto the first and second biocompatible attachment devices. The first andsecond biocompatible attachment devices are positioned, and the flexiblemember is adapted, so that the surgical implant applies a distractingforce between the superior and inferior vertebrae sufficient forselectively maintaining the first and second pedicles at a predetermineddistance.

In another embodiment, a facet replacement system is provided. The facetreplacement system includes a first posterior device having first andsecond attachment mechanisms and a compression-resistant memberconnected there between, and a second posterior device having first andsecond attachment mechanisms and an expansion-resistant member connectedthere between. The first attachment mechanisms are adapted to connect torespective portions of a superior spinous process, and the secondattachment mechanisms are adapted to connect to respective portions ofan inferior spinous process.

In another embodiment, a method for replacing functions of a facet jointbetween adjacent vertebrae is provided. The method includes: providingone or more flexible posterior devices to replace main functions of thefacet joint; and adapting a first one of the one or more posteriordevices for a first attachment to a first pedicle, and a secondattachment to a second pedicle.

In another embodiment, a prosthetic device for replacing functions of afacet joint between adjacent vertebrae comprises: means for providingone or more flexible posterior devices to replace main functions of thefacet joint; and means for adapting a first one of the one or moreposterior devices for a first attachment to a first transverse process,and a second attachment to a second transverse process.

In another embodiment, a method for replacing functions of a facet jointbetween adjacent vertebrae comprises: providing one or more flexibleposterior devices to replace main functions of the facet joint; andadapting a first one of the one or more posterior devices for a firstattachment to a first articular process, and a second attachment to asecond articular process.

In another embodiment, a method for replacing functions of a facet jointbetween adjacent vertebrae comprises: providing one or more flexibleposterior devices to replace main functions of the facet joint; andadapting a first one of the one or more posterior devices for a firstattachment to a first spinous process, and a second attachment to asecond spinous process.

In another embodiment, a method for replacing functions of a facet jointbetween adjacent vertebrae comprises: providing one or more flexibleposterior devices to replace main functions of the facet joint; andadapting a first one of the one or more posterior devices for a firstattachment to a first lamina, and a second attachment to a secondlamina.

In another embodiment, a method for replacing functions of a facet jointbetween adjacent vertebrae comprises: attaching one or more posteriordevices to the adjacent vertebrae to replace main functions of the facetjoint without utilizing any anatomical facet joint implant.

In another embodiment, a posterior device for replacing functions of afacet joint comprises: a first component comprising an elongated body;and a first joint having a first opening wherein the first openingcontains an elastic material; a second component comprising: anelongated body; and a second joint having a second opening wherein thesecond joint is coupled with the first joint, and the second openingcontains the elastic material; and a connector covering the first jointand the second joint wherein the connector comprises the elasticmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a posterior device and an anterior device forreplacing functions of a facet joint according to one embodiment of thepresent invention.

FIG. 2A illustrates a posterior device and an anterior device forreplacing functions of a facet joint according to one embodiment of thepresent invention.

FIGS. 2B and 2C illustrates exemplary posterior devices.

FIG. 3 illustrates posterior devices and an anterior device forreplacing functions of a facet joint according to one embodiment of thepresent invention.

FIG. 4 illustrates components of a posterior device for replacingfunctions of a facet joint according to one embodiment of the presentinvention.

FIG. 5 illustrates an assembled posterior device of FIG. 4.

FIGS. 6-8 illustrate exemplary usages of the posterior device of FIG. 5.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of theinvention, references will now be made to the embodiments, or examples,illustrated in the drawings, and specific languages will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. Furthermore,reference numerals are repeated for the sake of simplicity, and do not,by themselves, designate any combination of elements discussed in thedifferent embodiments. Any alterations and further modifications in thedescribed embodiments, and any further applications of the principles ofthe invention as described herein are contemplated as would normallyoccur to one skilled in the art to which the invention relates.

Referring now to FIG. 1, for the sake of example, two adjacent vertebraeV1 and V2 are shown with a damaged or degenerated facet joint 110. Thepresent embodiment attempts to replicate the functions (or somefunctions) of the facet joint 110 without necessarily requiring ananatomical implant such as a prosthetic facet joint device. It isunderstood, however, that an anatomical implant can still be used insome embodiments, as desired. To replace the functions of the facetjoint 110, a posterior device 100 and/or an anterior device 120 areutilized. The posterior device 100 may be utilized alone or may becombined with the anterior device 120 to replicate the functions of thefacet joint 110. Conversely, a stand along anterior device (without aposterior device) could be used to replicate the functions of the facetjoint.

To implement the functions of the facet joint 110 in the posteriordevice 100 and/or the anterior device 120, many methods may be employedto evaluate the functional requirements of the facet joint 110. Forexample, the spinal load carried by the facet joint 110 can bedetermined. Alternatively or in addition, motion analysis methods, whichutilize design devices to reproduce the motions of the facet joint 110,may be utilized.

Once the functional requirements of the facet joint 110 are evaluated,the composition of the posterior device 100 may be selected to meetthese requirements. Examples include flexible biocompatible devices,such as devices constructed of shape memory alloys, cables, or springs.In the illustration of FIG. 1, the posterior device 100 is a flexiblecable. In the present embodiment, the posterior device 100 may reside ina variety of physical locations, so that the device can be sized to meetthe functional requirements instead of meeting the space and shaperequirements of the facet joint 110. In this illustration of FIG. 1, theposterior device 100 is attached to the pedicles of the vertebrae V1 andV2 by biocompatible attachment devices 102 and 104, such as pediclescrews. Other examples of attachment devices include staples, rivets,and locking grooves formed within the vertebrae for receiving a securingportion of the device 100. It is contemplated that the posterior device100 may also be attached to other parts of the vertebrae V1 and V2, suchas articular processes, transverse processes, spinous processes, orlaminae. It is further contemplated that tethers, staples, and otheranchoring devices can be used.

The posterior device 100 may be a flexible cable that is made of shapememory materials, which may be polymer-based or Nitinol. For example,the posterior device 100 may comprise approximately half Ni and half Ti,and may be treated in hot air and then cold water to produce anaustenite finish temperature that is lower than the temperature range ofa human body. In this example, the posterior device 100 may have anaustenite finish temperature of approximately 34° C. Accordingly, atabove 34° C., the posterior device 100 becomes superelastic.

Prior to implanting the posterior device 100 into a human body, it maybe cooled to below 34° C. to maintain a predefined shape for easyinsertion. Alternatively, it may remain at a temperature of above 34°C., so that its superelasticity may assist the insertion.

The anterior device 120 may be inserted into a disc space between thevertebrae V1 and V2. In the illustration of FIG. 1, the anterior device120 is a disc replacement device, such as disclosed in U.S. Pat. No.6,402,785 (assigned to SDGI Holdings, Inc., and hereby incorporated byreference). Other examples of anterior devices 120 include flexiblebiocompatible devices, such as a cable, a spring, or a device made ofshape memory alloys.

Depending on the condition of the facet joint 110, it may or may not besurgically removed. For example, if the facet joint 110 causes severepain, then it may warrant removal. Alternatively, the facet joint 110may be left in place and may even be utilized to a limited extent.

Referring now to FIG. 2A, in another embodiment, a facet joint 204between vertebra V3 and V4 may be damaged or degenerated. As a result, aposterior device 200, which may be used alone, or combined with ananterior device 202, may replace the functions (or main functions) ofthe facet joint 204.

Referring now to FIG. 2B, in one embodiment, the posterior device 200may be a biocompatible spring that includes a pair of attachment devices206 and 208, a bias member 210, and a housing attachment 212.

The attachment devices 206 and 208 may comprises any conventionalattachment device, such as pins, connectors, cotters, rivets, spikes,keys, couplings, or bushings. In this illustration, the attachmentdevices 206 and 208 are biocompatible screws that may be inserted intothe vertebrae V3 and V4 to secure the posterior device 200.

The bias member 210 may reshape in response to spinal motions. Similarto the function of a conventional spring, the bias member 210 respondsto spinal movements by replicating the functions of the facet joint 204.For example, the bias member 210 may be compressed as a load is imposedupon the spine, but become extended during a flexion motion. It iscontemplated that the bias member 210 may operate within its elasticrange as determined by its chosen material and structure. It is furthercontemplated that the bias member 210 may comprise any biocompatiblematerial, such as titanium, carbon fiber, polymers, or shape memoryalloys.

The housing attachment 212 may be used to protect the bias member 210from the interference of surrounding tissues, so that the tissues willnot inadvertently clog the bias member 210 and impede its properfunction. It is contemplated that the housing attachment 212 maycomprise any biocompatible material, such as rubber or shape memoryalloys.

It is contemplated that the posterior device 200 and its components maycomprise a variety of shapes, such as the one illustrated in FIG. 2C. Itis further contemplated that the posterior device 200 may include aplurality of bias members, or that may simply be a conventional spring.It is also contemplated that the posterior device 200 may be anyflexible biocompatible device, such as a cable, or a device made ofshape memory alloys.

The posterior device 200 may be attached to the transverse processes ofthe vertebrae V3 and V4 by any conventional biocompatible attachmentdevices, such as pins, connectors, cotters, rivets, spikes, keys,couplings, bushings, washers, or other anchoring devices. It is alsocontemplated that the posterior device 200 may be attached to pedicles,articular processes, spinous processes, or laminae of the veterbrae V3and V4.

The anterior device 202, which may be a nucleus device, may be insertedinto a disc space between the vertebrae V3 and V4, and work togetherwith the posterior device 200 to replace the functions of the facetjoint 204. The anterior device 202 may comprise any conventional nucleusreplacement devices. Alternatively, it may comprise any flexiblebiocompatible device, such as a cable, a spring, or a device made ofshape memory alloys. It will be understood that conventional nucleusreplacement devices are known in the art, and will not be describedfurther herein.

Depending on the condition of the disc joint 204, it may or may not besurgically removed. For example, if the disc joint 204 causes severepain, it may be surgically removed. Alternatively, without substantiallyrelying on its functions, it may be left in the animal body.

Referring now to FIG. 3, in yet another embodiment, a combination of aposterior device 302 and a posterior device 304 may be used to replacethe functions (or main functions) of a damaged facet joint (not shown)between vertebrae V5 and V6. It is also contemplated that an anteriordevice 310, which may be similar to previously described devices 108 or202, may function together with the posterior devices 302 and 304 toreplace the facet joint functions.

The posterior device 302 and the posterior device 304 may complimenteach other in replicating the functions of the facet joint. For example,the posterior device 302 may be a biocompatible spring that regulatesthe capacity of the replaced facet joint functions, while the posteriordevice 304 may be a damper that regulates the movement of the replacedfacet joint functions. The posterior device 302 may be any of thepreviously described posterior device 100 or 200, or a biocompatibledamper. Likewise, the posterior device 304 may be any of the previouslydescribed posterior device 100 or 200. In one example, the posteriordevice 304 may be a damper identical or similar to the embodimentsdisclosed in the U.S. Pat. No. 2,235,488 entitled “Shock-AbsorbingDevice”, which is hereby incorporated by reference.

In this example, the posterior device 302 is attached to pedicles viapedicle screws, while the posterior device 304 is attached to transverseprocesses of the vertebrae V5 and V6. Alternatively, each of theposterior devices 302 and 304 may be attached to any of articularprocesses, transverse processes, spinous processes, laminae, or pediclesof the vertebrae V5 and V6. It is contemplated that one or moreadditional posterior devices may be added to the posterior devices 302and 304, and all of them may work together to replace the facet jointfunctions.

Even though previous embodiments are directed toward replacing thefunctions of a single facet joint, it is contemplated that thisinvention may be applied to replace the functions of a plurality offacet joints. For example, a bilateral approach may be adopted toreplace damaged facet joints on both sides of a disc.

Referring now to FIG. 4, in another embodiment, a posterior device 400may comprise a connector 418, a first component 420, and an secondcomponent 422. The posterior device 400 may be used alone, or incombination with one or more additional posterior and/or anteriordevices described previously, to replace the functions of a facet jointwithout any anatomical facet joint implant. It is contemplated that theposterior device 400 may be used to replace any of the posterior devices100, 200, 302 or 304 in the previously described embodiments.

The connector 418 provides elasticity for the posterior device 400 toallow motions that imitate the functions of a facet joint. The connector418 may comprise any elastic biocompatible material, such as rubber,silicon or shape memory alloys. It may comprise any suitable shape,which may be a hollowed olive or a partial sphere.

The first component 420 may comprise a tip 408, an elongated body 406,which may be a rod or shaft, and a joint 402. The tip 408 may bepointed, and adapted for a percutaneous insertion of the posteriordevice 400, which may entail pushing the posterior device 400 throughtissues of an animal body. The joint 402 comprises an opening 402, whichmay contain any biocompatible elastic material, such as rubber, siliconor shape memory alloys, to facilitate motions of the posterior device400.

The second component 422 may have an identical or similar structure asthat of the first component 420. In this illustration, the secondcomponent 422 may comprise a tip 416, an elongated body 414, which maybe a rod or shaft, and a joint 410. The tip 416 may be pointed, andadapted for a percutaneous insertion of the posterior device 400, whichmay entail pushing the posterior device 400 through tissues of an animalbody. The joint 410 comprises an opening 412, which may contain anybiocompatible elastic material, such as rubber, silicon or shape memoryalloys, to facilitate motions of the posterior device 400. The opening412 may be coupled to the opening 404, so that an elastic material mayflow through both openings 404 and 412 to facilitate the functions ofthe posterior device 400. It is also contemplated that the secondcomponent 422 may have a different structure from that of the firstcomponent 420.

The first and second components 420 and 422 may be coupled together byany conventional means, such as being molded or screwed together throughtheir respective joints 402 and 410, to form a unit. Further, they maybe coupled at different angles to simulate the natural anatomy of facetjoints. For example, to replace functions of a facet joint in thecervical region, the first and second components 420 and 422 may becoupled at approximately 45° to the horizon to simulate the orientationof a natural facet joint. In another example, to replace functions of afacet joint in the thoracic region, the first and second components 420and 422 may be coupled at an angle of approximately 60° to the axialplane and 20° to the frontal plane of a human body. In the lumbar area,the first and second components 420 and 422 may be joined at an angle ofapproximately 90° to the axial plane and 45° to the frontal plane of ahuman body.

Each of the first and second components 420 and 422 may comprise anybiocompatible material, such as stainless steel, titanium, shape memoryalloys, polymers, carbon fiber, and porous material. It is contemplatedthat the posterior device 400 may be attached to any of the pedicles,articular processes, transverse processes, spinous processes, or laminaeof vertebrae.

Referring now to FIG. 5, the posterior device 400 may be inserted intothe spinal region as a unit by any conventional approach, such as aposterior or lateral approach. It is also contemplated that theposterior device 400 may be inserted into the spinal region by theapproaches disclosed in the U.S. Pat. No. 6,530,929 (assigned to SDGIHoldings, Inc.).

Utilization of the posterior devices 100, 200, 302, 304, and 400 willnow be described. The posterior device(s) may be inserted into thespinal region by any conventional approach, such as a posterior orlateral approach. For example, procedures and instruments useable in aposterior approach are disclosed in U.S. Pat. No. 6,241,729 (assigned toSDGI Holdings, Inc.), and a publication by Sofamor Danek© 1996 entitled“Surgical Technique using Bone Dowel Instrumentation for PosteriorApproach”, each of which is incorporated herein by reference in itsentirety. It is also contemplated that any of the posterior devices 100,200, 302, 304, and 400 may be inserted into the spinal region by theapproaches disclosed in the U.S. Pat. No. 6,530,929 (assigned to SDGIHoldings, Inc., and hereby incorporated by reference).

The anterior devices 120, 202 and 303 may be inserted into the spinalregion by any conventional approach, such as an anterior, a posterior orlateral approach. For example, procedures and instruments useable in ananterior approach are disclosed in U.S. Pat. No. 6,428,541 (assigned toSDGI Holdings, Inc.), and the publication by Sofamor Danek© 1996entitled “Surgical Technique using Bone Dowel Instrumentation forAnterior Approach”, each of which is incorporated herein by reference inits entirety.

FIGS. 6-8 illustrate exemplary usages of the posterior device 400 as itis attached to the vertebrae of an animal body. For example, referringnow to FIG. 6, shown therein is the posterior device 400 placed betweenthe vertebrae V7, V8 by two multi-axial screws 602 and 604 according toone embodiment of the present invention. Further examples of attachmentmechanisms that can be used are disclosed in U.S. Pat. Nos. 6,280,442,5,891,145, 6,485,491, and 6,520,963, which are hereby incorporated byreference. FIGS. 7 and 8 illustrate perspective views of FIG. 6. fromdifferent angles to show the implementation of the posterior device 400according to one embodiment of the invention.

Although only a few exemplary embodiments of this invention have beendescribed above in details, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Also, features illustrated and discussedabove with respect to some embodiments can be combined with featuresillustrated and discussed above with respect to other embodiments. Forexample, attachment mechanisms secured to a spinal process canalternatively be secured to a pedicle or lamina, as desired.Accordingly, all such modifications and alternatives are intended to beincluded within the scope of the claimed invention.

1. A surgical implant comprising: a first biocompatible attachmentdevice configured to attach to a first pedicle of a superior vertebrae;a second biocompatible attachment device configured to attach to asecond pedicle of an inferior vertebrae; and a flexible member attachedto the first and second biocompatible attachment devices, the flexiblemember comprising a joint component and a flexible connector covering atleast part of the joint component; wherein the first and secondbiocompatible attachment devices are positioned, and the flexible memberis adapted, so that the surgical implant applies a distracting forcebetween the superior and inferior vertebrae sufficient for selectivelymaintaining the first and second pedicles at a predetermined distance.2. The surgical implant of claim 1 wherein the flexible member isfurther adapted to be compressed in response to a second force thatexceeds the distracting force.
 3. The surgical implant of claim 1wherein the joint component is positionable between the first and secondbiocompatible attachment devices, and comprises a first element having afirst opening and a second element having a second opening, and whereinelastic material is disposed between the first opening and the secondopening.
 4. The surgical implant of claim 1 wherein the flexible memberfurther includes a first member connected between the firstbiocompatible attachment device and the joint component, and a secondmember connected between the second biocompatible attachment device andthe joint component, and wherein the first and second members areconnected together at the joint component. 5.-29. (canceled)
 30. Aspinal stabilization device comprising: a first component comprising: anelongated body; and a first joint element having a first opening whereinthe first opening contains an elastic material; a second componentcomprising: an elongated body; and a second joint element having asecond opening wherein the second joint element is coupled with thefirst joint element, and the second opening contains the elasticmaterial; and a connector covering the first joint element and thesecond joint element wherein the connector comprises the elasticmaterial.
 31. The device of claim 30 wherein the first component furthercomprises a pointed tip adapted for percutaneous insertion of theposterior device.
 32. The device of claim 30 wherein the secondcomponent further comprises a pointed tip adapted for percutaneousinsertion of the posterior device.
 33. The device of claim 30 whereinthe connector is olive-shaped.
 34. The device of claim 30 wherein thefirst component and the second component are coupled at an angle ofapproximately 45.degree. to the horizon.
 35. The device of claim 30wherein the first component and the second component are coupled at anangle of approximately 60.degree. to an axial plane and 20.degree. to anfrontal plane of a human body.
 36. The posterior device of claim 30wherein the first component and the second component are coupled at anangle of approximately 90.degree. to an axial plane and 45.degree. to afrontal plane of a human body. 37.-39. (canceled)
 40. A spinalstabilization implant comprising: a first biocompatible attachmentdevice configured to attach to a first pedicle of a superior vertebrae;a second biocompatible attachment device configured to attach to asecond pedicle of an inferior vertebrae; and a flexible member attachedto the first and second biocompatible attachment devices, the flexiblemember comprising a first component and a second component and anelastic connector, the elastic connector covering at least a part of thefirst component or the second component; wherein when the first andsecond biocompatible attachment devices are attached to the first andsecond pedicles, the surgical implant applies a distracting forcebetween the superior and inferior vertebrae sufficient for selectivelymaintaining the first and second pedicles at a predetermined distance.41. The implant of claim 40, wherein the first component comprises afirst joint element and the second component comprises a second jointelement, and wherein the first joint element and the second jointelement are connected.
 42. The implant of claim 41, wherein the elasticconnector surrounds at least part of the first joint element and thesecond joint element.
 43. The implant of claim 40, wherein the firstcomponent comprises a tip adapted for percutaneous insertion of theimplant.
 44. The implant of claim 40, wherein the second componentcomprises a tip adapted for percutaneous insertion of the implant.
 45. Aflexible spinal stabilization device comprising: a first biocompatibleattachment device, a second biocompatible attachment device, a jointcomponent attached to the first and the second biocompatible attachmentdevice, the joint component comprising: a first elongated bodycomprising a first joint element having a first opening, and a secondelongated body comprising a second joint element having a secondopening, and a connector comprising a flexible material, wherein thefirst and second joint elements are covered by the connector and whereinelastic material is disposed between the first and second openings. 46.The implant of claim 45, wherein the first elongated body comprises atip adapted for percutaneous insertion of the implant.
 47. The implantof claim 45, wherein the second elongated body comprises a tip adaptedfor percutaneous insertion of the implant.